7508 Primary Hyperparathyroidism Caused By A CDC73-Related Atypical Parathyroid Tumor

Abstract Disclosure: R. Cardenas: None. S. Tariq: None. R. Habibi: None. N. Ebrahimi: None. E. Astiazaran-Symonds: None. Background: Primary hyperparathyroidism (PHPT) is a common endocrine disease, causes include: parathyroid adenomas (80-85%), parathyroid hyperplasia (10-15%), atypical parathyroid adenomas (APA) (1.2 %) and parathyroid carcinomas (PC) (1%). APA share many anatomic and histopathologic features with PC making the distinction between the two challenging. Although most are sporadic, some APA are caused by germline mutations in the CDC73 gene, which is associated with hyperparathyroidism-jaw tumor (HPT-JT) syndrome PC and familial isolated PHPT with APA. Clinical Case: A 42-year-old female presented to the clinic for evaluation of recurrent PHPT. She was diagnosed at age 22 when she experienced fatigue, polydipsia with hypercalcemia (12.9mg/dl). She underwent superior bilateral parathyroidectomy with pathology consistent with parathyroid adenoma. Twenty years later, symptoms recurred and tests showed hypercalcemia (13.0 mg/dl), elevated PTH (252 pg/dl), kidney function preserved (GFR: 82.5 ml/min), normal vitamin D 25 OH (31 ng/dl). Patient denied history of nephrolithiasis or fractures. Family history was positive for kidney stones in father and siblings, also history of a jaw tumor in niece. Sestamibi scan showed a left inferior parathyroid adenoma. Patient underwent resection of the adenoma; pathology revealed a left parathyroid adenoma with atypical parathyroid tumor, >95% cellularity with cytologic features concerning for malignancy, prominent macronucleoli, necrosis, elevated mitotic activity and Ki67 with 15% tumor cells without vascular invasion. Post-op Calcium and PTH normalized (9.6 mg/dl and 10.8 pg/ml, respectively). Genetic testing via multi-gene panel identified a whole gene deletion of CDC73, consistent with hyperparathyroidism-jaw tumor syndrome. Panoramic jaw x-rays did not show jaw tumors. Genetic testing for family members is underway. Conclusion: Although somatic mutations in CDC73 are frequently found in sporadic APA and PC, germline mutations are a rare cause of PHPT associated with these tumors. Histopathological examination is necessary to confirm the diagnosis of APA and to differentiate it from PC, which has a recurrence rate >50%. APA should be treated as a “tumor of uncertain malignant potential” and needs to be carefully and periodically followed up with measurement of Ca, PTH and vitamin D. Confirmation of a CDC73 mutation by genetic testing helped identify the increased risk for other associated tumors in jaw, kidneys and uterus prompting initiation of surveillance with panoramic jaw x-rays with neck shielding, renal US and pelvis US. Genetic testing of family members will allow timely detection and treatment of individuals at risk. Presentation: 6/3/2024